The invention is related to a method for the detection of an exceeding of a limiting value in a radioactivity measurement.
In the measurement of radioactive contaminations, the measurement values are compared with a limiting value which results from regulatory and legal prescriptions, respectively. Due to the nature of radioactive radiation, the measurement values are subject to periodical variations. Therefore statistical certainties are used for the measurement of a contamination, which are related to the so-called background measurement and the event measurement. In doing this, it is known to establish the duration of measurement in dependence of the necessary statistical certainty, the resulting limiting value and the value of the background measurement. The duration of measurement for the fulfilment of the statistical certainty is thus predefined already before the beginning of the actual measurement, and is calculated from the aforementioned parameters. The measurement value for the predetermined duration of measurement is determined and compared with the limiting value for the measurement value. If the measurement value is above the limiting value, an exceeding of the limiting value is stated. With the known method, it is disadvantageous that comparatively long durations of measurement result, even when there is no contamination (net measurement rate).
From DE 42 40 535, a method is known for fast detection of a radiation source with a gamma line, moving in relation to the receiver.
From U.S. Pat. No. 3,670,164, a plutonium detector for persons is known. With the plutonium detector, the background radiation is continuously measured by a number of gamma detectors. The measured value is used as the actual value for the background radiation upon the entrance of a person into the detection zone, and accounted for in the measurement.
The invention has the objective to provide a method for the detection of an exceeding of a limiting value, which promptly and reliably indicates the occurrence of an exceeding of a limiting value.